Well, I just installed ISPConfig 3.0.5 RC1, very interesting version. It solves a lot of problems like now I can choose if the user may use SSL.
But still, I can't figure out how to configure SSL on one IP-address. it's still not working, even in 3.0.5 RC1 I can't get it to work properly with multiple sites on 1 IP address. Can someone please explain how I have to configure it?